Mozilla yesterday released a first beta of its next browser, Firefox 18, touting a revamped JavaScript engine and support for Macs with Apple's higher-resolution "Retina" displays.

Firefox 18 is currently slated to ship in final form the week of Jan. 7, 2013.

Top of the improvement list, Mozilla said, was the new JavaScript JIT (just-in-time) compiler, dubbed "IonMonkey" in keeping with naming conventions that have pegged predecessors as "TraceMonkey" and "JaegerMonkey."

IonMonkey, which was first added to Firefox in mid-September with the "Nightly," or roughest, build of version 18, boasts new technology that allows Mozilla's browser to render complex JavaScript -- like that used by online games or Web-based applications -- significantly faster than previous JIT compilers.

Depending on the performance benchmark, IonMonkey speeds up Firefox's JavaScript rendering by between 7% and 26%, claimed David Anderson, a Mozilla engineer on the JIT compiler team, in a Sept. 12 blog post.

Other improvements in Firefox 18 highlighted by Mozilla included support for the "Retina" screens used by some Apple MacBook Pro notebooks, a browser-integrated PDF viewer, and an option that lets users disable insecure content -- that not protected by SSL, in other words -- found on HTTPS-secured sites.

That last feature has a possibly record-breaking history: According to Bugzilla, Mozilla's change- and bug-tracking database, work on insecure content disabling began almost 12 years ago, four years before Firefox 1.0 appeared.

"Way to go. I thought this might never land. And we beat the 12-year anniversary!" said Johnathan Nightingale, Mozilla's vice president of engineering, in a September 2012 message on the Bugzilla thread devoted to the feature.

The beta of Firefox 18 can be downloaded from Mozilla's website. Users who have been running earlier betas will be automatically updated to the new preview.